Brood Enlargement and Post-Natal Development in the Black Noddy Anous minutus

Abstract

The ability of the Black Noddy to raise an artificially enlarged brood and the effect of brood enlargement on prefledging growth and mortality were examined on Heron Island during the 1983-84 breeding season. Where chicks from enlarged broods were the same age brood enlargement did not affect nestling growth or mortality. This suggests adults were able to compensate for the increased energy requirements of a second brood member. Reproductive output from enlarged broods was not limited by the total quantity of food available, or by the ability of adults to find and transport this food. Where chicks were different ages intra-brood competition reduced the amount of food obtained by younger chicks, causing a retardation of flight feather development. A slowing in wing development was not accompanied by a reduction in the rate of weight increase. Feather development slows before starvation is apparent; this suggests wing growth may be modified so that nutrients essential for body maintenance and the growth of soft tissue are available during periods of low food availability. In the Black Noddy maximum body weight is attained significantly earlier than full wing length. Differences in the rate of weight and wing length increase, the ability of adults to raise an enlarged brood and the further slowing of only feather development during food stress, suggest that 'normal' wing development in this species may be adjusted to some minimum level of a fluctuating food resource, rather than to consistently low levels of food availability. Such a mode of development can be interpreted as an adaptive response to large variations in the quantity of food obtained at any one feeding andlor the extended period of time between consecutive feeding bouts.